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Scientists plan to use the “clocks” of dead stars to illuminate the most mysterious things in the universe: dark energy.
These timekeepers are actually pulsars, or rapidly spinning neutron stars born when stars at least eight times the size of the sun die. The extreme conditions of neutron stars make them ideal laboratories for studying physics in environments found nowhere else in the universe.
So-called “millisecond pulsars” can spin hundreds of times a second and blast beams of electromagnetic radiation from their poles like cosmic lighthouses, which sweep across space. They get their name because when they were first seen, these neutron stars seemed to pulsate, increasing in brightness when their beams were aimed directly at Earth.
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The ultraprecise timing of the millisecond brightness variation of pulsars means that they can be used together as cosmic timepieces in “pulsar-timing arrays.” These arrays are so precise that they can measure gravitational disturbances in the fabric of space and time, unified as a four-dimensional entity called “space-time,” which could be an ideal way to detect dark matter. hunting
“Science has developed very precise methods for measuring time,” pulsar timing researcher John LoSecco, of the University of Notre Dame, said in a statement. “On Earth, we have atomic clocks, and in space, we have pulsars.”
Calling time on the dark matter mystery
Dark matter is so mysterious because it does not interact with light or normal matter – or, if it does, it does so very weakly and we cannot detect it. “Normal matter” consists of atoms made up of electrons, protons and neutrons that interact with light and matter, so scientists know that dark matter must be made of other particles.
Despite not interacting with light, dark matter has a gravitational influence, and its presence can be inferred when this influence affects light and indeed ordinary matter. It is the effect of this gravitational influence on light that LoSecco and his colleagues aimed to exploit in pulsars.
According to Albert Einstein’s theory of general relativity, objects with mass and spacetime curve, and gravity results from this curvature. When light passes through this curve, its path is also diverted. This can change the travel time of light, causing light from the same distant body to reach Earth at different times, theoretically “slowing it down” (the speed of light is not actually changed; it is the distance it travels which changes ).
Dark matter has mass, so concentrations of this mysterious form of matter can also warp space-time. Therefore, the path of light from distant objects is curved, and its arrival time is delayed when it passes through a concentration of dark matter. This effect is called “gravitational lensing,” with the intervening body changing the path of light called “gravitational lensing.”
LoSecco and colleagues examined data collected from 65 pulsars in the Parkes Pulsar Timing Array. They observed about 12 events that showed variations and delays in the timing of the pulsars, which typically have nanosecond precision.
This suggests that the radio wave beams from these dead star cosmic beacons are traveling around densely in space due to an invisible concentration of mass somewhere between the pulsar and the telescope. The team theorizes that these invisible masses are candidates for dark matter “clumps.”
“We take advantage of the fact that the Earth is moving, the sun is moving, the pulsar is moving, and even dark matter is moving,” said LoSecco. “We take into account the deviations in the arrival time due to the change in the distance between the mass we are observing and the line of sight to our pulsar ‘clock’.”
The whole team looks very different. To demonstrate this, a body with the mass of the sun would cause a delay of about 10 microseconds in pulsed radio waves. The team has seen the proposed dark matter delay deviations 10,000 times less than that.
“One of the results suggests a distortion of about 20% of the sun’s mass,” said Professor LoSecco. msgstr “This object may be a candidate for dark matter.”
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One side effect of the team’s research is to improve the accuracy of Parkes Pulsar Timing Array data, which is collected to look for evidence of low-frequency gravitational radiation.
Dark matter clumps can add interference, or “noise,” to this data; identifying and removing that noise will help scientists make better use of this sample set in their search for low-frequency leaks in spacetime called gravitational waves. This could enable the detection of gravitational radiation from more distant and therefore earlier black hole mergers – and, perhaps even the initial gravitational waves of the background left over from the Big Bang.
“The true nature of dark matter is a mystery,” LoSecco said. “This research sheds new light on the nature and distribution of dark matter in the Milky Way and may also improve the accuracy of precise pulsar data.”
The team’s findings were presented at the National Astronomy Meeting (NAM) 2024 meeting at the University of Hull on Monday (July 15).
